Multi-blades fan device

ABSTRACT

A multi-blade fan having a fan assembly including a bottom plate and a plurality of circumferentially spaced blades and a casing for the fan assembly therein having an outlet duct extending therefrom for discharge of the air flows. The fan assembly includes an annular shroud connected to the axial ends of the blades remote from the bottom plate. The casing includes a bottom wall for rotatably connecting the fan assembly, a top wall for defining an air inlet for axially introducing the air into the casing, and a tubular wall connecting the bottom and top walls. The top wall of the casing adjacent to the inlet opening forms an annular projection having a bell cross sectional shape opened inwardly so that an axial end of the shroud extends thereto. The bell cross section portion radially extends to a portion that is inclined downwardly in the outward direction, which faces the shroud so that a small gap extending radially is created. The top wall or bottom wall of the casing at its radially outer portion can be downwardly inclined. The tubular wall of the casing can also be inclined so that the bottom end of the tubular wall is spared radially outward from its center.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal type fan, which isparticularly suitable for use in an air conditioning apparatus of anautomobile.

2. Description of a Related Art

Known in a prior art is a multi-blade fan device as disclosed in theJapanese Un-Examined Patent Publication No. 2-146298 and JapaneseUn-Examined Patent Publication No. 2-151519, where a fan assembly havinga plurality of blades is stored in a fan casing defining an inlet(mouth) for air introduced into the casing by the rotational movement ofthe fan assembly.

Such a prior art fan device is defective in that its operational noiseis high and its fan efficiency is low due to the creation of turbulencein the casing because of the occurrence of a reverse flow or vortex.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a multi-blade fandevice with an improved construction capable of avoiding the abovementioned drawbacks existing in the prior art.

According to a first aspect of the invention, a fan device is provided,comprising:

a casing having a tubular body portion having axially spaced first andsecond end walls and a tubular side wall connecting the first and secondend walls to each other, and a discharge duct connected to the bodyportion;

the first wall having an opening that is coaxial with respect to theaxis of the casing;

a fan assembly arranged in the casing so that a passageway is created inthe casing around the fan assembly so that the width of the passagewaygradually increases in the circumferential direction until thepassageway is connected to the duct, and;

said fan assembly being constructed by a base plate rotatably supportedby the casing at the second wall, a plurality of blades fixedlyconnected to the outer periphery of the base plate so that the bladesare circumferentially spaced, and an annular shroud connected to theedges of the blades spaced from the base plate;

said first wall forming a first portion, adjacent to said opening,having an recessed cross sectional shape;

the first wall having a second portion extending radially outwardly fromsaid first portion; said second portion being arranged adjacent to theshroud of the fan assembly so that a small, annular gap is createdbetween the guide portion of the casing and the shroud of the fanassembly.

According to the second aspect of the invention, a fan device isprovided, comprising:

a casing having a tubular body portion having axially spaced first andsecond end walls and a tubular side wall connecting the first and secondend walls to each other, and a discharge duct connected to the bodyportion;

the first wall having an opening that is coaxial with respect to theaxis of the casing;

a fan assembly arranged in the casing so that a passageway is created inthe casing around the fan assembly so that the width of the passagewaygradually increases in the circumferential direction until thepassageway is connected to the duct;

said fan assembly being constructed by a base plate rotatably supportedby the casing at the second wall, and a plurality of blades fixedlyconnected to the outer periphery of the base plate so that the bladesare circumferentially spaced;

said first wall being inclined toward the second wall in a radiallyoutward direction.

BRIEF EXPLANATION OF ATTACHED DRAWINGS

FIGS. 1-(A) and (B) are partial cross sectional shapes of a fan devicein the prior arts, respectively.

FIG. 2A is a cross sectional view of an air conditioning device for anautomobile to which the fan device according to the present invention isapplied.

FIG. 2B is a schematic side view of a fan device according to thepresent invention illustrating its scroll shaped casing, taken alongline B--B in FIG. 2A.

FIG. 3 is an enlarged cross sectional view of the fan assembly accordingto the present invention.

FIG. 4 shows the relationship between a flow factor and a specific noiseand pressure factor in the first embodiment, in comparison with theprior art.

FIG. 5 shows the relationship between a gap-to-fan diameter ratio andfan efficiency and minimum specific noise.

FIG. 6 shows the relationship between a flow factor and specific noiseand a pressure factor with respect to various positions of the inneredge of the bell shaped mouth of the shroud.

FIG. 7 shows the relationship between a flow factor and specific noiseand a pressure factor with respect to various positions of the top edgeof the shroud.

FIGS. 8 to 13 are similar to FIG. 3, but illustrate various otherembodiments of the present invention, respectively.

FIG. 14 is a relationship between the flow angle and the angle of theportion of the bottom wall in FIG. 13.

FIG. 15 is similar to FIG. 2A but shows a different embodiment, where atop and bottom wall of the fan casing are inclined.

FIG. 16 is a partial enlarged view of the cross section of the fandevice in FIG. 15.

FIGS. 17 and 18 are similar to FIG. 16, but show different embodimentsof the invention, respectively.

FIG. 19 is a perspective view of a fan device of 10th embodiment in FIG.18.

FIGS. 20 and 21 are similar to FIG. 16, but show different embodimentsof the invention, respectively.

FIG. 22 shows the relationship between a flow factor and specific noiseand a pressure factor in the embodiment in FIG. 17.

FIG. 23 shows the relationship between the inclination angle of thebottom wall and fan efficiency and the minimum specific noise withrespect to the embodiment in FIGS. 16 and 17.

FIG. 24 shows the relationship between the inclination angle of the topwall and fan efficiency and the minimum specific noise with respect tothe embodiment in FIGS. 16 and 17.

FIG. 25-(A) corresponds to FIG. 16, but illustrates a relationshipbetween the air flow angle and the inclination of the top and bottomwalls.

FIG. 25-(B) shows the relationship between the air flow angle and theoptimum wall inclination angles.

FIG. 26 is a partial cross sectional view of the fan device of adifferent embodiment of the present invention.

FIG. 27 is a side view of the fan casing taken along line XXVII in FIG.26.

FIG. 28 illustrates the arrangement of the side wall of the fan casingwith respect to the blades for various values of the scroll angle in theembodiment in FIG. 26.

FIG. 29 shows the relationship between the scroll angle and theinclination angle.

FIGS. 30, 31 and 32 are similar to FIG. 26, but show differentembodiments of the invention respectively.

DESCRIPTION OF PREFERRED EMBODIMENTS

A problem to be solved by the present invention will be explained withreference to FIGS. 1-(a) and 1-(b), which show constructions of acentrifugal fan for an air conditioning apparatus of an automobile inthe prior arts. FIG. 1-(a) shows a partial arrangement of a fan assemblyin a prior art. The fan assembly is constructed by a centrifugal fan 20having a plurality of circumferentially spaced blades 25 between abottom plate 24 and a top or retaining ring 42 having an L crosssectional shape, and a casing 21 for storing the fan 20. The casing 21has a top wall 211 defining a central inlet (mouth) 36 opened axiallywith respect to the fan 20, so that the rotational movement of the fan20 causes the air to be drawn into the fan 20 fan via the inlet opening36 as shown by arrows 48, and to be directed radially outwardly as shownby arrows 49 between the blades 25.

Tests conducted by the inventor on the prior art have revealed thatreverse flows between the tip end 42b and the inner surface 43a of thecasing 21, as shown by an arrow 101, and reverse flows or vortexes atthe upper part of passageways between the blades 25 or at the locationradially outwardly of the retainer ring 42, as shown by arrows 102, 103and 104, are apt to occur. These reverse flows or vortexes occurindependently from the amount of blown air, thereby reducing theoperational stability of the fan, and wasting the driving power of thefan. Furthermore, turbulence are apt to occur in the drawn air flows viathe inlet 36 or the discharged air flow, thereby increasing theoperational noise and reducing the fan efficiency.

Furthermore, tests conducted by the inventor have also revealed that, inthe prior art construction, a velocity distribution along the height ofthe blades is as shown by a line V, which means that a substantial flowof air is only locally obtained at the bottom portion of the spaceinside the casing 21, and the upper portion of the space inside thecasing 21 is a dead space 38, whereat an air flow does not substantiallyoccur. Such a dead space 38 necessarily may generate a vortex on onehand, and increase the operational noise and reduce fan efficiency onthe other hand.

Also known in the prior art is a fan device as shown in FIG. 1-(b),where a plurality of circumferentially spaced blades are arrangedbetween a bottom plate 24 and a retainer ring 42 as an annular flatplate connected to the top edges of the blades 25.

The problems as mentioned with reference to FIG. 1-(a) also occur in theprior art construction in FIG. 1-(b). Namely, the reverse flows as shownby arrows 51 and 52 are apt to be generated and a vortex as shown byarrow 50 is generated at the top portion of the space inside the casing21. Furthermore, the air flow distribution along the vertical length ofthe blades is as shown by an a line V', which means that a uniform airflow can not be obtained along the entire length of the fan.

In FIG. 2A, which shows an air conditioning apparatus for an automobile,a reference numeral 1 denotes a duct assembly, which forms an outsideair inlet 2 for introducing an amount of external air (not shown), andan inside air inlet 3 for introduction of an amount of internal air. Afan assembly 6 is arranged inside the duct 1 for generating a forcedflow of air introduced into the duct via the inside air inlet 2 or theoutside air inlet 3. The fan assembly 6 is constructed by a fan case 21provided with an air inlet 36, a centrifugal fan 20 subjected to arotating movement for drawing axially an amount of air flow via theinlet 36 and for discharging the air radially outwardly, and an electricmotor 33 connected to the fan 20 for imparting a rotational movement tothe fan 20. The air flows as radially discharged from the fan 20 are,via an outlet duct 37, directed to an evaporator 7 arranged in the duct1 at a position located downstream from the fan assembly 6. Theevaporator 7 is a heat exchanger for obtaining a heat exchange betweenthe air in the duct and a refrigerant passing through the evaporator 7.The evaporator 7 is provided with an inlet 7-1 for the refrigerant andan outlet 7-2 for the refrigerant. A switching damper 5 is arranged inthe duct 1 so that it moves between a position 5A (solid line) where theoutside air inlet 2 is closed, and the inside air inlet 3 is opened forintroduction of the inside air from the cabin into the duct 1 as shownby an arrow F₁, and a position 5B (dotted line) where the inside airinlet 3 is closed and the outside air inlet 2 is opened for introductionof air outside the cabin into the duct 1, as shown by an arrow F₂.

An air mix damper 8 is arranged in the duct 1 at a position locateddownstream from the evaporator 7 so that the air mix damper 8 createsfirst and second air passageways 18 and 19. The air mix damper 8controls the ratio between the amount of air passing through the firstpassageway 18 and the amount of air passing through the secondpassageway 19 in accordance with the degree of the opening of the airmix damper 8. A heater core 17 is arranged in the second passageway 19and is connected to a hot water source, such as engine cooling water, sothat a heat exchange is obtained between the air in the duct 1 and thehot water in the heater core 17, for heating the air passing through thesecond air passageway 19. The heater core 17 has an inlet 17-1 and anoutlet 17-2 for the hot water. The first and second air passageways 18and 19 are, at their downstream ends, combined to an air mix chamber 9.Opened to the air mix chamber 9 is a lower outlet 10 for discharging airflows directed to the lower parts of a passenger, an upper outlet 12 fordischarging air flows directed to the upper parts of a passenger, andtop outlets 13 for discharging air flows directed to the top parts ofthe cabin. Dampers 14, 15 and 16 are provided for controlling the flowof air from the outlets 10, 12 and 13, respectively.

FIG. 3 shows a detailed construction of the fan assembly, which isconstructed, basically, by the centrifugal fan 20 and the casing 21. Thecasing 21 is constructed by an upper part 22 and a lower part 23, whichare made as a mold from a certain plastic resin material. The upper andlower parts 22 and 23 are formed with faced flange sections 22-1 and23-1, which are connected to each other by suitable means, such asclamps or bolts and nuts. The casing 21 together with an outlet duct 37forms, as shown in FIG. 2B, a scroll shape. Namely, the outlet duct 37extends tangential from the casing 21. In the casing 21, a scrollpassageway 40 is created radially outward from the fan 20, and theradial width of the scroll passageway 40 is from a nose point Ngradually increasing in the circumferential direction up to a locationwhere the scroll passageway 40 is connected to the duct 37.

In FIG. 2A, the electric motor 33 for operating the fan 20 has a housingconnected to the bottom of the casing 21 and a rotating shaft (notshown) connected to the fan 20 for imparting a rotational movementthereto. As shown in FIG. 3, the fan 20 is constructed by a bottom plate24 having a central boss portion 28, a plurality of blades 25, eachextending axially from the bottom plate 24, and a shroud 26 as astrengthening ring plate connected to the ends of the blades 25.Connected to the boss portion 28 of the fan 20 is a rotating shaft (notshown) of the fan 20 (FIG. 2) for imparting a rotational movement of theshaft to the fan 20. It should be noted that, as shown in FIG. 3, thebottom plate 24 is convexed axially upward from the outer peripheralportion 242 to the center portion 241. The blades 25 are connected tothe outer peripheral portion 242 of the bottom plate 24 of the fan 20,and these blades are arranged along the circumference of the outerperiphery 242 of the bottom plate 24 so that they are equiangularlyspaced. As shown in FIG. 3, a shroud member 26 has an axially extendingannular projection 261 extending from the top edges of the blades 25.The annular projection 261 has an inner surface that is located on thesame radius as that of the outer periphery of the bottom plate 24, sothat a division line 30 for a mold is created. It should be noted thatthe shroud 26 has an outer annular portion 263 having a smoothly curvedcross sectional shape extending radially and outwardly while inclinedtoward the bottom wall of the casing to which portion 263 the top edgesof the blades 25 are connected.

The casing 21, in which the fan assembly 22 is stored, forms an innercircular portion (mouth) 31, inwardly of which, the axial inlet 36 forthe air to be drawn is created. The portion 31 forms, along its crosssection, a bell shaped (semicircular) cross section, to which thetubular projection 261 of the shroud 26 extends, and located around themouth 31 is an intermediate portion 221 that is inclined downwardlywhile facing the portion 263 of the shroud 26, so that a spacing δ of avalue of about 3 mm is created between the faced annular surfaces of theportion 263 of the shroud 26 and the portion 221 of the top wall of thecasing 21. Such an annular spacing of about 3 mm with respect to thecasing 22 extends along the entire radial extension of the curved uppersurface 263 of the shroud 26, namely up to the outer peripheral end 264of the shroud 26.

As shown in FIG. 3, the intermediate portion 221 radially and outwardlyextends to an outer top wall portion 222 extending in a plane transverseto the axis of the rotation of the fan 20.

The lower casing 23 has a bottom wall 231 extending in a planetransverse to the axis of the rotation of the fan 20. The upper casing22 has a tubular outer wall 223 connected to the outer end of the topwall 222 up to the flange portion 22-1, while the lower casing 23 has atubular outer wall 233 extending from the outer end of the bottom wall231 up to the flange portion 23-1

The casing according to the first embodiment is constructed by the upperand lower casings 22 and 23 having tubular walls 223 and 233, which forma tubular outer wall when they are connected to each other via theflanges 22-1 and 23-1.

An operation of the first embodiment as explained above will beexplained with reference to that in the prior art. A rotation of the fan20 causes the air to be drawn in the direction substantially axially asshown by the arrows 48. The drawn air flow gradually changes to a radialdirection, and finally flows radially, as shown by the arrows 49,between the blades 25 to the scroll chamber 40. According to the presentinvention, a small long gap δ is created between the faced surfaces ofthe shroud 26 and the top wall of the casing 21, so that a reverse flowis prevented, and a smooth flow of air from the inlet 36 to the bladesis obtained. As a result, efficiency is increased and there is a lowlevel of noise. Contrary to this, in the prior art as shown in FIG.1-(a), a reverse flow, as shown by an arrow 101, is apt to be generateddue to the fact that only a limited length small gap is located betweenthe retainer 42 and the inner surface of the casing 21, thereby reducingthe fan efficiency and increasing the operational noise.

According to a visualized test using a spark tracing method, the priorart construction can obtain a velocity distribution of air as drawn viathe inlet opening 36, as shown by a line V in FIG. 1-(a) such that theair flows are, as shown by the arrows 49, apt to be concentrated at alower portion of the blades 25, and only a limited amount of air flow isobtained at the upper portion of the blades 25. Thus, a slight increasein flow resistance causes a vortex or reverse flows, as shown by anarrows 102 and 103, to occur in the upper part of the blades 25.

Contrary to this, according to the present invention, as shown in FIG.3, a shroud 26 at the top of the blades 25 extends along the directionof the air flows 48 as drawn from the inlet opening 36, while the upperwall 221 of the casing of the constant small spacing of δ with respectto the shroud 26 extends in the same direction, which is very effectivefor preventing reverse flows in the prior art.

The provision of the shroud 26 having this construction is veryeffective in obtaining flows of air having substantially equalizedspeeds from the top end to the bottom end of the outer peripheral edgeof the fan, as shown by a line V" in FIG. 3, which effectively preventsreverse flows from being generated.

According to the test conducted by the inventors, an increase in fanefficiency of about 3 percent and a decrease in the noise level for 1.5dB can be realized, over the construction in the prior art as shown inFIG. 1- (a) .

The centrifugal flow type fan is suitable for use in an air conditioningapparatus of an automobile in that a large amount of air flow can beobtained irrespective of a small value of static pressure. In the priorart fan of this type as shown in FIGS. 1-(a) and (b), a distribution ofthe air flow speed along the axial length is shown by a curve V or V',providing an area 38 in the upper space inside the casing 21, where noair flow is substantially created other than a vortex 104. The vortex asgenerated causes the air flows 49 as discharged to be turbulent, therebyincreasing operational noise, and reducing efficiency. Contrary to this,according to the invention as shown in FIG. 3, the dead space in theprior art in FIG. 1-(a) and (b) is eliminated due to the limited spacebetween the faced surfaces of the shroud and the casing having a spacingδ. As a result, a smooth flow of air is obtained, thereby preventingvortex from occurring in the casing 21. Thus, fan efficiency can beincreased, while reducing operational noise.

Result of tests conducted by the inventors will now be shown withreference to the embodiment in FIG. 3, where the outer diameter of thefan 20 is 150 mm, the axial length of the fan 20 was 85 mm, the angle ofthe spread of the scroll was 5.5°, the voltage of an electric currentapplied to the blower motor 33 was a constant 12 volts, and the ratio ofthe gap δ between the shroud and the casing to the outer diameter of thefan is 0.02. In FIG. 4, an abscissa indicates a flow factor Φ, and anordinate indicates a specific noise K_(s) as well as a pressure factorΨ. In FIG. 4, dotted lines show the results of the present invention(first embodiment in FIG. 3), and solid lines show the result of theprior art, as shown in FIG. 1-(a). The results in FIG. 4 show that, overthe prior art, the present invention can reduce the noise and increasethe pressure factor K_(S).

In FIG. 5, abscissa is a ratio of the gap δ to the fan diameter, and anordinate is fan efficiency η_(F) and the minimum specific noise K_(s) asthe minimum value of K_(s) upon a change in the flow factor Φ. As can beseen from FIG. 5, a value of the ratio of the gap to the fan diametersmaller than a value of about 0.05 results in significantly reducedvalue of the minimum specific noise K_(s).

According to the first embodiment in FIG. 3, a test is also done so asto obtain an effect of the position of the inner edge of the bell mouth31 of the casing 21 with respect to the outer edge of the shroud 26 byproviding samples of various positions of the inner edge of the bellmouth with respect to the outside edge of the shroud 26. Namely, in FIG.6, according to the first sample, the inner edge of the bell mouth 31extends until it locates a position A₀, where a ratio of the spacing 1between the inner edge of the casing and the blade 25 to the outerdiameter D of the fan 1-D ratio) is 0.02. In the second sample, theinner edge of the bell mouth 31 extends up to a position as shown by A₁,where the value of the 1-D ratio is 0.04. Actual values of the spacing 1for the first and second samples were 3 mm and 6 mm, respectively. Inthe case of the third sample, the inner edge of the bell mouth portion31 extends up to a position designated by A₂, where the inner edge ofthe bell mouth 31 is in a common plane similar to that of the inner endsurface 261 of the shroud 26. For the fourth sample, the inner edge ofthe casing terminates at a location A₃, where no bell mouth portion iscreated, so that the inner edge extends only axially so as to obtain thesame axial end position as the axial end portion B₀ of the shroud 26. InFIG. 6, an abscissa is a flow factor φ, an ordinate is specific noiseK_(s) and pressure factor Ψ. With respect to various combinations ofpositions of the inner edge A₀, A₁, A₂, and A₃, and B₀, relationshipsbetween the flow factor φ and specific noise K_(s) and between the flowfactor φ and the pressure factor Ψ are shown. As will be easily seen,the least amount of noise occurs when the position of the edge of thetop wall of the casing is A₀. Thus, the best position for the inner edgeof the bell shaped mouth is such that the spacing of the edge withrespect to the blade is as small as possible, so that a smooth flow ofair is obtained between the faced walls of the shroud and the casing,thereby reducing the operational noise.

Now, the effect of the position of the top edge of the shroud withrespect to the bell mouth portion 31 will be discussed. In FIG. 7, threedifferent positions B₀, B₁ and B₂ of the top edge of the shroud areobtained. Namely, for the positions B₀, B₁ and B₂, the ratio of thetheir height h to the outer diameter D of the fan 20 were 0.06, 0.03 and0.0, respectively. Namely, for the positions B₀, B₁ and B₂, the value ofthe height h were 9 mm, 4.5 mm and 0.0 mm, respectively. In FIG. 7, theposition of the inner edge of the bell mouth portion 31 was A₀, whichhas already been explained with reference to FIG. 6. In FIG. 7, anabscissa is flow factor φ, an ordinate is specific noise K_(s) andpressure factor Ψ. With respect to various combinations of positions ofthe inner edge A₀, and B₀, B₁ and B₂, relationships between the flowfactor φ and specific noise K_(s) and between the flow factor φ and thepressure factor Ψ are shown. As will be easily seen, the least amount ofnoise occurs when the position of the edge of the shroud portion is B₀.Thus, the best position for the inner edge of the bell shaped mouth issuch that the spacing of the edge 26B of the shroud 26, with respect tothe faced inner surface of the bell mouth portion 31, is as small aspossible, so that a reverse flow of air is effectively prevented fromoccurring, which effectively reduces the operational noise. It should benoted that the result of the test in FIGS. 4 and 5 are obtained when theposition of the outer edge of the bell mouth is A₀ and the position ofthe axial edge of the shroud is B₀.

In a second embodiment in FIG. 8, the shroud 26 extends only to theupper edge of the blades 25, so that no axial projection 26b, as is thecase in the previous embodiment is provided. As a result, a constantradial gap δ is created between the shroud 26 and the top wall of thecasing 21.

In a third embodiment in FIG. 9, the bottom plate 33 of the fan 20extends up to the outer radius of the blades 25. Namely, the bottomplate 33 and the shroud 26 have the same value as the outer radius. Inthis case, the bottom plate 33 and the blades 25 are made as one piece,and the shroud is connected to the blade at a later stage.

In a fourth embodiment in FIG. 10, the bell mouth inwardly extends onlyto a position 31b corresponding to the top edge 26b of the axial innerprojection of the shroud 26. This construction can provide a large areaof the inlet opening 36 of the casing, thereby increasing the amount ofintake air.

In a fifth embodiment in FIG. 11, the portion 263 of the shroud 26connected to the top edge of the blades 25 is formed as a conical shapedefining a radially, downwardly inclined straight line in its crosssection. The casing 21 has a conical shaped portion 221 faced with theconical shaped portion 263 of the shroud so that a substantiallyconstant gap δ is created between the faced conical walls of the shroudand the casing 21.

In a 6th embodiment in FIG. 12, the fan is provided with a bottom plate24 having an outer peripheral portion 24-1 extending downwardly andinclining under an angle θ with respect to the horizontal plane. The airflows, as shown by arrows are, when passed through the blades 25, guidedby the portion 24-1, thereby reducing turbulence. Thus, provision ofthis shape of the bottom plate 24 in combination with the bell mouthshaped inner edge 31 can effectively reduce operational noise.

In 7th embodiment in FIG. 13, the bottom wall of the casing 21 isconstructed by a flat, central plate portion 52 located just below thefan 20, an intermediate annular portion 54 having a conical shape anddefining, in cross-section, a straight line inclined downwardly in theradially outer direction at an angle θ_(s), and an annular outer flatportion 53 extending from the intermediate conical portion 54. The outerflat portion 53 is connected to the tubular side wall portion of thecasing 21. Such a casing construction 21 can provide a scroll shaped airpassageway of which the cross section increases gradually as it movestoward the outlet of the passageway.

In the 7th embodiment in FIG. 13, a relationship between the inclinationangle θ_(s) of the portion 54 and the inclination angle of the air θ_(f)as issued from the blades 25 is shown. Namely, in FIG. 14, an abscissais the inclination angle θ_(s) of the plate portion 54 and an ordinateis the inclination angle θ_(f) of the air flow. In FIG. 14, an optimuminclination angle θ_(s) is such that it provides the smallest value ofthe minimum specific noise k_(s), It should be noted that the fanefficiency η_(f) has such a relationship with respect to the minimumspecific noise k_(s) that the smaller the minimum specific noise k_(s),the higher the fan efficiency η_(f). As a result, the optimuminclination angle θ_(s) can be determined in accordance with the fanefficiency value η_(f).

According to the test in FIG. 14, various fans having different air flowinclination angle values θ_(f) are provided, and tests have been done onthe fans. In FIG. 14, the desired range of inclination angle θ_(s) is ina range, as shown by shaded lines, which is between a straight lineexpressed by an equation θ_(s) =θ_(f) (.sup.° ) and a straight lineexpressed by an equation θ_(s) =θ_(f) -5(° ).

FIG. 15 is similar to FIG. 2A but directed to an 8th embodiment of thepresent invention. This 8th embodiment in FIG. 15 differs in that, inplace of the top and bottom wall of the casing extending in a planetransverse to the axis of the rotation of the fan 20, the top and bottomwall of the casings have radially outer portions 222 and 232 that areinclined downwardly. Construction other than this point is the same asthat in FIG. 2A, and therefore, a detailed explanation thereof will beomitted using the same reference numeral for parts functioning in asimilar way.

FIG. 16 shows a detailed construction of the fan assembly in the 8thembodiment, which is constructed, basically, by the centrifugal fan 20and the casing 21. The casing 21 is constructed by an upper part 22 anda lower part 23, which are made as a mold from a certain plastic resinmaterial. The upper and lower parts 22 and 23 are formed with facedflange sections 22-1 and 23-1, which are connected to each other by asuitable means, such as clamps or bolts and nuts.

As shown in FIG. 16, the fan 20 is constructed by a bottom plate 24having a central boss portion 28, a plurality of blades 25, eachextending axially from the bottom plate 24 while forming a curved plateinclined with respect to the direction of the rotation of the fan 20,and a shroud 26 as a strengthening ring plate connected to the ends ofthe blades 25. Connected to the boss portion 28 of the fan 20 is arotating shaft (not shown) of the fan 20 for imparting a rotationalmovement from the shaft of a motor 33 (FIG. 15) to the fan 20. It shouldbe noted that, as shown in FIG. 16, the bottom plate 24 is convexedaxially upward from the outer peripheral portion to the center portion.The blades 25 are connected to the outer peripheral portion 242 (FIG.16) of the bottom plate 24 of the fan 20. These blades are arrangedalong the circumference of the outer periphery 242 of the bottom plate24 so that they are spaced equiangularly. As shown in FIG. 16, theshroud member 26 has an inner annular axially projected portion 262,which is located on the same radius as that of the outer periphery ofthe bottom plate 24, so that a division line 30 for a mold is created.It should be noted that the shroud form, on the outer side thereofspaced from the blade portion 25, has an annular top curved surface witha substantially arc shaped cross section.

The casing 22, in which the fan assembly 22 is stored, forms an innercircular edge 31, inwardly of which the axial inlet 36 for the air to bedrawn is created. The inner circular edges 31 form, along its crosssection, a bell mouth shaped portion defining an annular recess, towhich the tubular projection 262 of the shroud 26 extends, so that a gapof a spacing δ of a value of about 3 mm is created between the facedsurfaces of the shroud 26 and the inner wall 311 of the bell mouthportion 21 of the casing 22. Such an annular gap of about 3 mm withrespect to the casing 22 extends along the entire radial extension ofthe curved upper surface 263 of the shroud 26; namely from the top endof the axial projection 262 to the outer peripheral end 264.

As shown in FIG. 16, the casing 22 has a top wall 222 extending alongthe shroud 26 of the fan 20 while maintaining a small spacingtherebetween. Furthermore, the top wall 222 is downwardly inclined as itis located radially outward, so that an angle θ₁ is created between thehorizontal plane that is transverse to the axis of rotation of the fanand the upper wall 222 of the casing 22.

The lower casing 23 has a central part 231 extending horizontally up toa location corresponding to the outer diameter of the blades 25, i.e.,the outer edge 264 of the shroud 26, and a peripheral part 232 locatedoutside of the central part 231; part 232 extends up to a lower edge 234of the lower casing 23, while inclining downwardly under an angle θ₂with respect to the horizontal plane. In other words, the upper surface222 and the lower surface 232 of the casing are both inclined downwardlyat the angle θ₁ and θ₂, respectively, in the same direction as they arelocated radially outward.

The casing according to the 8th embodiment is constructed by the upperand lower casings 22 and 23 having tubular walls 223 and 233, whichconstruct a tubular outer wall when they are connected to each other viathe flanges 22-1 and 23-1.

According to the 8th embodiment in FIG. 16, similar to the firstembodiment in FIG. 3, a shroud 26 at the top of the blades 25 extendsalong the direction of the air flows 48 as drawn from the inlet opening36 while the upper wall 222 of the casing of the constant spacing of δ,with respect to the shroud 26, extends along the same direction for adistance longer than the extension of the shroud. Such a constructionvery effectively prevents reverse flows in the prior art.

According to the inventor's test, in the prior art shown in FIG. 1-(a)of (b), a portion of the bottom wall 212 of the casing extendingoutwardly of the fan 20 causes the air flows 49 to come into contactwith said portion 212, thereby causing turbulence in the air flows.According to the 8th embodiment in FIG. 16, the bottom wall of thecasing has an outer portion 232 outside the diameter of the fan 20,which is inclined downwardly with respect to the horizontal wall at anangle θ₂, similar to the top wall 222 of the casing 21. As a result, theair flows from the blades 25 are prevented from colliding with thebottom wall portion 232, thereby reducing operational noise, with theconstruction according to the present invention.

FIG. 17 shows a partial view of a 9th embodiment, wherein a centrifugalfan device includes a normal type of fan 20 with no shroud that issimilar to the fan in the prior art shown in FIG. 1-(b), this normaltype of fan with no shroud is arranged in the casing 21 having a pair ofopposite top and bottom walls 222 and 232 having the same constructionas shown in FIG. 16 in the 8th embodiment, which are both inclineddownwardly outward with respect to the horizontal plane as they arelocated radially. Namely, the fan 20 in the 9th embodiment in FIG. 17 isprovided with a plurality of circumferentially spaced blades 25 having arectangular shape connected at their top end by means of a ring shapedretainer ring 42. In this 9th embodiment, the upper wall of the casing21 has an inner mouth 31 formed as an inwardly opened bell shape havinga semi-circular shape. Extending radially outward from the mouth 31 is atop wall portion 222 that is inclined, with respect to a horizontalplane, at an angle θ₁ . Similar to the 8th embodiment, the casing in the9th embodiment in FIG. 17 has a bottom wall having a center portion 231extending horizontally up to a diameter corresponding to the diameter ofthe fan 20 and a radially outward portion 232 extending from the centralportion 231 at an angle θ₂ with respect to the horizontal plane.

A 10th embodiment of the present invention is described with referenceto FIG. 18 together with a perspective view of the centrifugal fan inFIG. 19. This embodiment is modified, with respect to the 9th embodimentin FIG. 17, in that the upper wall 222 of the casing inclineddownwardly, with respect to the horizontal plane at an angle θ₁, extendssmoothly to the edge portion 31 of an arc shaped cross section. Similarto the 9th embodiment in FIG. 17, the casing 21 has a bottom outerportion 232 extending from the outer diameter of the blades 25, which isinclined downwardly with respect to the horizontal plane at an angle θ₂.

FIG. 19 shows, in a perspective view, a scroll shaped casing 21, for the10th embodiment in FIG. 18. The fan casing 21 is formed as a scrollhaving a tubular body portion in which the fan assembly 20 is rotatablystored, and which has an axis of elongation that is parallel to the axisof the rotation of the fan assembly 20, and a outlet duct portion 37extending tangentially from the tubular body portion. The fan assembly20 is constructed of a bottom plate 24, a plurality of circumferentiallyspaced blades 25 fixedly connected to the outer periphery of the bottomplate, and a retainer ring connected to the top ends of the blades 25.The tubular body portion has a top wall 222 having an inlet 36 axiallyopened to the fan assembly 20, a bottom wall 232 that is axially spacedfrom the top wall 222, and a tubular side wall connecting the top andbottom walls 222 and 232 to each other. The outlet duct 37 forms arectangular cross sectional shape having a top wall 37-1 extending fromthe top wall 222 of the tubular portion, a bottom wall 37-2 extendingfrom the bottom wall 232 of the tubular portion, and side walls 37-3 and37-4 extending from the tubular walls of the tubular portion 27. The fanassembly 20 is stored in the casing 21 so that a space 40 commencingfrom a nose point N having an increased radial dimension is createdalong the direction of the rotation of the fan assembly; the space ofwhich is connected to the outlet duct 37. Such a space having anincreased radial dimension can receive a desired amount of air inducedby the fan, which increases circumferentially from the nose point N. Therotation of the fan assembly 20 causes the air to be drawn via the inletopening 36, and the drawn air is directed radially outward via theblades into a space inside the casing 21 radially outward from the fanassembly 20, and is directed to the outlet duct 37. As is also explainedwith reference to FIG. 18, the top wall 222 in FIG. 19 has an innerannular edge 31 for defining the inlet opening 36 from which it isinclined downwardly at an angle θ₁ with respect to the horizontal plane.The bottom wall 232 has an outer peripheral portion extending from aposition of the radius of the fan assembly, the portion of which isinclined downwardly at an angle of θ₂ with respect to the horizontalplane.

FIG. 20 shows a 11th embodiment, which is similar to the 8th embodimentin FIG. 16, except that the ring shaped shroud 26 has an inner topportion 262 extending smoothly from the remaining portion adjoining theblades 25 so that the top portion is slightly radially and downwardlyinclined with respect to the axis of the rotation of the fan 20, andexcept that the upper wall 222 of the casing 21 is formed with a curved(inner) portion 222-1 extending outwardly from the edge portion 31 alongthe shroud 26 of the fan assembly 20 so that a gap having a constantwidth δ is created between the faced surfaces of the shroud and the topwall, a bent (middle) portion 222-2 extending vertically downward to alocation corresponding to the outer diameter of the blades 25 at theirradial outermost end, and a peripheral (outer) portion 222-3 bent fromthe middle portion 222-2 and extending downwardly so as to form an angleθ₁ with respect to the horizontal plane. As similar to the previousembodiments (8th to 10th embodiments), the casing 21 has a bottom wallhaving an outer portion 232 located radially outward from the outerdiameter of the blades 25; the portion 232 of which extends downwardlyso as to form an angle θ₂ with respect to the horizontal plane.

FIG. 21 shows a 12th embodiment where a shroud 35 is formed with anannular base portion 350 contacting the top edges of the blades 25, andthe portion 350 extends radially downward to form, along thelongitudinal cross section, a straight line in place of the curved linein previous embodiments. In the 12th embodiment in FIG. 21, the casinghas a top wall defining an inner edge portion 31 defining a bell shapedcross section, an inner portion 222-1 extending radially while incliningdownwardly, and the inner portion 222-1 forming along its cross sectiona straight line so that a substantially constant gap of δ is createdbetween the faced surfaces of the portions 350 of the shroud 35 and theportion 222-2 of the top wall of the casing 21. Similar to the 11thembodiment in FIG. 20, a provision is also made for a bent (middle)portion 222-2 extending vertically downward to a location correspondingto the outer diameter of the blades 25 at their radial outermost end,and a peripheral (outer) portion 222-3 bent from the middle portion222-2 and extending downwardly so as to form an angle θ₁ with respect tothe horizontal plane. Similar to the previous embodiments (8th to 11thembodiments), the casing 21 has a bottom wall having an outer portion232 located radially outward from the outer diameter of the blades 25;the portion 232 of which extends downwardly so as to form an angle θ₂with respect to the horizontal plane.

Results of tests conducted by he inventors will now be shown withreference to the 9th embodiment in FIG. 17, where the outer diameter ofthe fan 20 is 150 mm, the axial length of the fan 20 is 85 mm, the angleof the spread of the scroll is 5.0°, the voltage of an electric currentapplied to the blower motor 33 is a constant 12 volts, and the values ofthe angles θ₁ and θ₂ of the inclination of the top and bottom wallportions 222 and 232 are both, 10°. In FIG. 22, an abscissa indicates anflow factor Φ, and an ordinate indicates a specific noise K_(s) as wellas a pressure factor Ψ. In FIG. 22, dotted lines show the results of thepresent invention, and solid lines show the results of the prior art, asshown in FIG. 1-(b). The results in FIG. 22 show that, over the priorart, the 9th embodiment in FIG. 17 can reduce the noise up to 3 to 4 dBand increase the pressure factor K_(s).

A test was also done to check the effect of the values of theinclination angles θ₁ and θ₂ over the minimum specific noise K_(s) and afan efficiency η_(f). The test was done under the same conditions asmentioned above with reference to the test shown by FIG. 22. Note, theminimum specific denotes the value of the specific noise that providesthe minimum value of the specific noise when the value of the flowfactor φ is varied. In FIG. 23, an abscissa is the inclination θ₂ of theouter portion 232 of the bottom wall of the casing 21, and an ordinateis the minimum specific noise as well as the fan efficiency η_(f). Theresult in FIG. 23 was obtained when the value of the θ₁ is maintained to20°. In FIG. 24, an abscissa is the inclination θ₁ of the portion 222 ofthe top wall of the casing 21, and an ordinate is the minimum specificnoise as well as the fan efficiency η_(f) . The result in FIG. 24 isobtained when the value of the θ₂ is maintained to 20°. In FIGS. 23 and24, solid lines denote the results of the 9th embodiment in FIG. 17 ofthe present invention, while the dotted line shows the results of the8th embodiment in FIG. 16. It is clear from the results in FIG. 22 thatthe minimum value of the specific noise level K_(s) is about 20 dB forthe construction of the fan device in the prior art shown in FIG. 1-(b).On the other hand, as can be seen from the results in FIGS. 23 and 24, aminimum specific noise K_(s) of a value about 15.8 dB (point a) isobtained when the upper surface inclination angle θ₁ =20° and lowersurface inclination angle θ₂ is 0° for the 8th embodiment (FIG. 16), asshown by the dotted lines, which means that the construction of the 8thembodiment of the present invention in FIG. 16 can reduce the noiselevel of about 4.2 dB even with a construction in that only the top wall222 is inclined with respect to the horizontal plane, while the lowerplate 232 remains horizontal when compared with the construction of theprior art in FIG. 1-(b). Similarly, for the 9th embodiment (FIG. 17) asshown by the solid lines in FIGS. 23 and 24, a minimum specific noiseK_(s) of a value about 16.0 dB (point b) is obtained when the uppersurface inclination angle θ₁ =0° and lower surface inclination angle θ₂=20° for the 8th embodiment (FIG. 16), as shown by the dotted lines. Forthe 9th embodiment in FIG. 17, a reduction in the noise level of about4.0 dB can be obtained, compared to the construction in the prior art inFIG. 1-(b).

In the 9th embodiment (FIG. 17), as shown by the solid lines in FIG. 23,a minimum specific noise K_(s) when θ₁ and θ₁ =0° is 16.4 dB. This meansthat the construction of only the upper wall portion 222 as inclined canobtain a reduction of noise level of 0.4 dB over the construction of noinclination.

In addition to the inclination θ₁ at the top wall 222, the provision ofthe inclination θ₂ at the bottom wall 232 can further effectively reducethe minimum specific noise K_(s). The desired range of angle θ₂ valuesfor the minimum specific noise is in a range between 5° to 20° for the8th embodiment, shown by the dotted line in FIG. 23, and between 5° to30° for the 9th embodiment, shown by the solid line in FIG. 23.

As will be seen from FIG. 24, illustrating the effect of the angle θ₁ ofthe inclination of the top wall 222 upon a fixed value of the angle θ₂of the inclination of the bottom wall 232. The desired range of angle θ₁values for the minimum specific noise is in a range between 5° to 20°for the 8th embodiment, shown by the dotted line in FIG. 24, and between5° to 40° for the 9th embodiment, shown by the solid line in FIG. 24.

If the fan efficiency η_(f) is focused, as in the 9th embodiment in FIG.17, when the top and bottom wall inclination angles θ₁ and θ₂ have avalue of zero, the value of the fan efficiency η_(f) is raised to about57%, and when the value of the top wall inclination angle θ₁ ismaintained at 20°, as shown in FIG. 23, the 9th embodiment, as shown bythe solid line with the bottom wall inclination angle θ₂ value in arange between 0° to 30°, can produce a fan efficiency value η_(f) largerthan the 57% value of the fan efficiency η_(f) that is obtained whenboth the top and bottom wall inclination angles θ₁ and θ₂ are equal tozero. When the bottom wall inclination angle θ₂ is maintained to 20°, asshown in FIG. 24, the 9th embodiment, as shown by the solid line with atop wall inclination angle θ₁ value in a range between 5 to 30°, canproduce a fan efficiency value η_(f) larger than the 57% fan efficiencyvalue η_(f) that is obtained when both the top and bottom wallinclination angles θ₁ and θ₂ are equal to zero.

As regards the minimum specific noise K_(s) and the fan efficiencyη_(f), it is preferable that the top wall inclination angle θ₁ be in arange between 5° to 30° while the bottom wall inclination angle θ₂ be ina range between 5° to 40°.

FIG. 25-(a) is the same as the 8th embodiment (FIG. 16) but explains arelationship between the angle θ_(f) of the air flow issued from the fan20 and the top or bottom wall angle designated as θ_(s) in FIG. 25-(a)but corresponding to θ₁ or θ₂ in FIG. 16. The air flow angle θ_(f) ismeasured with respect to the horizontal plane. In FIG. 25-(a), where thefan 20 provides a flew of air that forms an angle θ_(f) with respect tothe horizontal plane, the most suitable inclining angle θ_(s) hereinreferred to is an angle θ₁ or θ₂ of the top plate 222 or the bottomplate 232, with respect to the horizontal plane, which can provide thedesired result. This most suitable inclining angle θ_(s) is, forexample, the 8th embodiment in FIG. 16, the angle θ₂ of about 10°, whichcan provide the smallest specific noise value K.sub. s , as shown inFIG. 23. Proportional, substantially, to the minimum specific noiseK_(s) is the fan efficiency η_(f), and therefore the most suitableinclination angle θ_(s) can be determined in accordance with the valueof the fan efficiency value η_(f).

The tests by the inventors were conducted by changing the height h ofthe blades 25 of the fan to obtain various air discharging angle θ_(f)values. In FIG. 25-(b), an abscissa is the value of the air dischargingangle θ_(f), and an ordinate is the value of a suitable inclinationangle θ_(s). As can be seen from FIG. 25-(b), the suitable inclinationangle θ_(s) is in a range as shown by the shaded lines, which is locatedbetween a line L₁ expressed by an equation θ_(s) =θ_(f) -5 and a line L₂expressed by an equation θ_(s) =θ_(f).

FIG. 26 (13th embodiment) is a modification of the 8th embodiment inFIG. 16, where the top and bottom walls of the casing are inclineddownwardly in the radially outward direction of the casing. As shown inFIG. 26, the casing 21 is constructed of a top wall, a bottom wall, anda tubular side wall connecting the top and bottom walls. The top wall isconstructed of an inner bell shaped portion 31, and an outer ring shapedportion 222 that is inclined downwardly toward the radially outwarddirection at an angle θ₁. The bottom wall is constructed of a centralportion 231 extending horizontally, and an outer portion 232 that isinclined downwardly toward the radially outward direction at an angleθ₂.

FIG. 27 is a schematic side view of the casing shown along a line XXVIin FIG. 26. As explained with reference to FIG. 2B, the casing 21 isformed with a scroll shape having a tubular body portion and a ductportion 37 extending tangentially from the body portion. The fan 20having an axis O₁ of rotation, so that a scroll passageway 40 of agradually increasing width toward the outlet duct 37, is created in thecasing 21 outside of the fan 20. As shown in FIG. 27, the casing forms anose 220 having a rounded shape at a location where the outlet duct 37is connected to the tubular body portion. The center of the curvature ofthe nose portion 220 is designated by O₂. A line X for connection of thecenter O₁ of the rotation of the fan 20 with the center O₂ of thecurvature of the nose 220 is referred to, herein, as a reference line(θ=0). The angle (scroll angle) θ is defined as an angle of the positionof the casing about the center O.sub. 1 measured from the reference lineX. At a location of the casing 21 in a range of the angle θ between 0°and 45° (line X'), the outer tubular side wall extends parallel alongthe axis of the rotation of the fan 20, as shown in FIG. 28-(a) or (b).In other words, an angle α of the plane of the side wall with respect tothe line parallel to the axis of the rotation of the fan is zerodegrees. At a location of the casing in a range of the angle θ between45° to 270°, the value of the angle α is increased in accordance with anincrease in the scroll angle. See FIGS. 28-(c), (d) and (e). FIG. 29shows a relationship between the scroll winding angle and the value ofthe angle α of the inclination of the side, tubular wall of the casing.At a location of the casing in a range of the angle θ between 270° to360°, the value of the angle α is maintained to 8°. See FIG. 28, (a) to(e). Such a shape of the outer side, tubular wall of the casing iseffective for obtaining a value in the casing in accordance with the airamount therein, which corresponds to the velocity distribution of theradial air flows via the spaces between the blades 25 from the air inletport 35. FIG. 28 (a) to (e) shows respectively desired values of theside wall angle α when the value of the scroll angle θ is 0°, 45°, 90°,180° and 270°, respectively. Such an arrangement is advantageous inpreventing so-called reverse flows, which otherwise occur when an airflow from the blades contacts the surface 22c of the case 21, elevatingflows, which otherwise occur due to the pressure difference between thetop and the bottom of the blades 25, and recirculating flows, whichotherwise occur at the region adjacent to the air inlet 36. As a resultof the elimination of reverse flows, elevating flows and therecirculating flows, turbulence in the air flows in the casing areprevented, noise is reduced, and the efficiency of the fan is increased.

According to the 13th embodiment in FIG. 26, the air as drawn from theinlet opening 36 inwardly of the bell mouth portion 31 is passed betweenthe blades 25, as shown by arrows in FIG. 28-(a), in such a manner thatthe direction of the air flows is gradually changed from an axialdirection, to a radial direction, so that the air flows are finallydischarged from the blades substantially radially as shown by arrows.The inclination of the side wall at the angle α, with respect to avertical line, is a predetermined range of scroll winding angle θvalues, so that smooth flows of air after passing through the blades areobtained and directed toward the outlet duct 37.

According to the test conducted by the inventor using the spark tracingmethod, which visualizes a flow rate distribution at the outlet of theblades 25, as shown in FIG. 28, larger the value scroll angle θ, andlarger the speed of the air flow at the bottom portion. Namely, when θis 0°, the velocity distribution at the outlet of the blade issubstantially uniform as shown by a line L_(a). When the scroll angle θis 45°, the flow speed distribution is as shown by a line L_(b), so thatthe speed of the air flows at the bottom level becomes higher than thatat the top level. When the scroll angle θ is 90° and 180°, respectively,the air speed at the bottom level is much faster, as shown by line L_(c)and L_(d), respectively. Finally, when the scroll angle θ is 270°, thespeed distribution at the bottom level is as shown by a line L_(e), sothat the difference in the air velocity at the bottom portion from thatat the top portion is large. Thus, it can be concluded that, at a regionof scroll angle θ values larger than a predetermined value, such as 90°,a substantial flow of air takes place only at the bottom portion of theblades, while air flow at the top portion of the blades is very small.Thus, the arrangement of the side wall of the casing as inclined at anangle α, the value of which increases in accordance with an increase inthe scroll angle θ, can produce a smooth flow of air from the bladesinto the outlet duct 37, while preventing air flows after passingthrough the blades from colliding with the upper surface 22_(c) bottomwall of the casing, thereby preventing reflection of the flows, asmentioned with reference to the prior art. Simultaneously, theinclination angle α of the tubular side wall of the casing is increasedin accordance with an increase in the change of speed between the bottomand top in velocity distribution, so that the pressure differencebetween the top and bottom portion of the blades can be reduced. As aresult, the occurrence of an elevated flow of air in the casing isprevented, which will otherwise occur due to the existence of thereverse flows and the pressure difference.

A 14th embodiment in FIG. 30 is similar to the 10th embodiment in FIG.18, but an inclination of the side wall of the casing is provided,similar to the embodiment in FIG. 26.

FIG. 31 shows 15th embodiment that is similar to the 1st embodiment inFIG. 3, but an inclination of the side wall of the casing is provided,similar to the embodiment in FIG. 26.

FIG. 32 is a 16th embodiment that is a modification of the 15thembodiment in FIG. 31 in that the bottom wall of the casing has an outerperipheral portion that is inclined downwardly in a radially outwarddirection.

We claim:
 1. A fan device comprising: a casing having a tubular bodyportion having axially spaced first and second end walls and a tubularside wall connecting the first and second end walls, and a dischargeduct connected to the body portion;the first wall having an opening thatis coaxial with respect to the axis of the casing; a fan assemblyarranged in the casing so that a passageway is created in the casingaround the fan assembly so that the width of the passageway is graduallyincreased in the circumferential direction until the passageway isconnected to the duct; said fan assembly being constructed by a baseplate rotatably supported by the casing at the second wall, a pluralityof blades fixedly connected to the outer periphery of the base plate sothat the blades are circumferentially spaced, and an annular shroudconnected to edges of the blades spaced from the base plate; said firstwall forming a first portion, adjacent to said opening having a curvedcross sectional shape; and the first wall having a second portionextending radially outward from said first portion, said second portionbeing arranged adjacent to the shroud of the fan assembly; the firstwall having a third portion, and an intermediate portion interconnectingsaid second and third portions, said third portion extending radiallyoutwardly from the intermediate portion to the tubular side wall; thefirst and the second portions creating, along an axial cross section, asmoothed profile portion extending along the shroud, which forms, withrespect to the shroud, a small annular gap of substantially constantvalue along substantially an entire radial length of the shroud.
 2. Afan device according to claim 1, wherein said first portion forms aninwardly open bell shaped cross-section, and said shroud forms anannular projection that extends toward a recess of said bell shapedfirst portion.
 3. A fan assembly device according to claim 1, wherein aratio of the dimension of said gap to the outer diameter of the fan issmaller than a value of 0.05.
 4. A fan device according to claim 1,wherein said second wall extends entirely in a plane that is transverseto the axis of the rotation of the fan assembly.
 5. A fan deviceaccording to claim 1, wherein said base plate forms a center portion forreceiving a drive force for rotating the fan assembly, and an outerannular portion extending radially outward from the center portion andinclining toward a bottom wall of the casing in a radially outwarddirection.
 6. A fan assembly according to claim 1, wherein said secondwall of the casing forms a central portion extending in a plane that istransverse to the axis of the rotation of the fan assembly up to aradial position corresponding, substantially, to an outer diameter ofthe fan assembly, an annular middle portion extending from the centralportion that inclines away from said first wall in a radially outwarddirection, and an annular outer portion extending in a planesubstantially transverse to the axis of the rotation of the fanassembly.
 7. A fan assembly according to claim 1, wherein said shroudhas at least an annular plate portion faced with the said second portionof the first wall of the casing; said annular plate portion extendingradially outward while being inclined toward the second wall of thecasing.
 8. A fan device according to claim 7, wherein said first wall isinclined and an angle O₁ of inclination of the first wall with respectto a plane transverse to an axis of rotation of the fan assembly is in arange between 5° to 30°.
 9. A fan device according to claim 8, whereinsaid second wall forms a central portion extending in a plane that istransverse to the axis of the rotation of the fan assembly up to aradial position corresponding, substantially, to an outer diameter ofthe fan assembly, and an annular peripheral portion that is inclined inthe same direction as the first wall.
 10. A fan device according toclaim 9, wherein an angle θ₂ of inclination of the annular peripheralportion is in range between 5° to 40°.
 11. A fan device according toclaim 8, wherein the value of the angle θ₁ of said inclination of thefirst wall corresponds to the angle of the air flow discharged via theblades by the rotational movement of the fan assembly.
 12. A fan devicecomprising:a casing having a tubular body portion having axially spacedfirst and second end walls and a tubular side wall connecting the firstand second end walls to each other, and a discharge duct connected tothe body portion; the first wall having an opening that is coaxial withrespect to the axis of the casing; a fan assembly arranged in the casingso that a passageway is created in the casing around the fan assembly sothat the width of the passageway is gradually increased in thecircumferential direction until the passageway is connected to the duct;said fan assembly being constructed of a base plate rotatably supportedby the casing at the second wall, and a plurality of blades fixedlyconnected to the outer periphery of the base plate so that the bladesare circumferentially spaced; and said first wall being inclined towardthe second wall in a radially outward direction, the second wall beinginclined in the radially outward direction, at a degree which issubstantially equal to that of the first wall, the inclination of thefirst and second walls being such as to correspond to the direction ofair flow discharged via the blades by the rotational movement of the fanassembly.
 13. A fan device according to claim 12, wherein said fanassembly further comprises an annular shroud arranged at ends of theblades spaced from the base plate; the shroud forming along its crosssection a smoothly changed profile inclined toward the second wall ofthe casing in the radially outward direction; the shroud being arrangedin facing relation to an inner surface of the first wall such that asmall annular gap extends radially outward.